The invention relates to an apparatus and method for producing building foundations from poured concrete, particularly an essentially reusable concrete foundation form apparatus and method of use.
Poured concrete foundations for buildings have been used for many years and usually require disposable formwork such as lengths of lumber and plywood sheets, which are temporarily installed on the ground or site surfaces. Installing conventional foundation forms is a time-consuming, labour-intensive task and is often conducted in poor conditions of loose topsoil and/or rocks etc. These conditions are often aggravated by rain or ground water which further destabilizes the soil and commonly requires pumping prior to pouring the concrete. Preferably, such foundations are installed on relatively level ground or site surfaces, and the above difficulties are compounded when the site is not level, i.e. it slopes in one or more directions. Installation costs increase because a sloping site usually requires additional excavation to level the site prior to installing foundation forms.
When a single storey building is to be built on a level site, sometimes relatively simple foundations can be installed. Simple foundations usually require a footing with or without a relatively low wall extending thereabove to receive longitudinal horizontal timbers upon which the building can be erected. On the other hand, a foundation for a building with a basement usually requires a footing with a relatively high basement wall extending upwardly therefrom, the basement wall having a width typically between one half and one quarter of the width of the footing, depending on building code requirements. A footing combined with a high wall is commonly made in two stages, the first stage being the preparation of the footing form and footing by itself. After the first pour of concrete has set to produce the footing, wall forms are erected above the footing to receive the second pour of concrete to form the wall itself. This two-stage type of foundation is relatively time consuming because it requires relatively close control of the locations of two sets of the form members to ensure compliance with building code requirements.
Both types of foundation formwork described above use lengths of lumber and plywood sheets which, after stripping from the set concrete, are contaminated with concrete and thus are usually unsuitable for use elsewhere in the building, except perhaps in low-grade or temporary construction work. Consequently, when constructing conventional concrete foundation forms, there is usually a high labour input both in installing the forms and stripping the forms after pouring the concrete, and there is also high wastage of form material when the poured foundation has been stripped.
U.S. Pat. No. 5,224,321 discloses an earlier invention of the present applicant in which a foundation form assembly is secured to a temporarily supported prefabricated floor assembly. The foundation form assembly extends downwardly from the floor assembly towards a building site surface which supports jacks which in turn temporarily support the floor assembly. The form assembly comprises inner and outer rigid sheet panels which serve as upper forms and are connected to the floor assembly. Lower portions of the rigid sheet panels are connected to upper edges of a flexible fabric sheet lower form element which rests on the site surface and extends as a generally U-shaped elongated container between the inner and outer sheet forms. The flexible fabric sheet form conforms to undulations of the site surface when it receives a flowable concrete mixture, and thus accommodates variations in height between the form and the site surface, thus reducing work required to prepare the site surface. Form ties extend between the inner and outer rigid forms to restrict movement thereof and to resist forces from the concrete before it sets. The poured concrete has an upper surface in contact with the floor assembly to provide permanent support therefor. When the concrete sets, the jacks are removed and the outer rigid sheet forms can be removed or can remain in place. This patent discloses a flexible sheet form element which provides a footing to accommodate site undulations and slope, and while it has many advantages over prior art foundation structures, the time for installing and levelling the prefabricated floor assembly and attaching the rigid sheet forms thereto increases the cost of both materials and labour when compared with the present invention.
German Patent Publication 2062998, in which the applicant is Beton-U. Monierbau AG, discloses several embodiments of poured concrete foundations in which a flexible fabric sheet form is located adjacent or beneath a temporarily supported component, and thus resembles to some extent the device of the above patent. In one embodiment, upper edges of the fabric sheet form are connected to the component to provide an elongated container below the component to receive flowable concrete, which when set supports the component. The sheet form assumes a shape determined to some extent by optional stiffeners positioned within the form, but not connected thereto, or other constraints located externally of the sheet form. This invention is particularly applicable for providing foundations for structure to be supported above a body of water.
Both of the references discussed above use a flexible fabric sheet form element which permits the footing to conform to the site surface, but require restraining structure to maintain the sheet form element in place and to attempt to control shape of the flexible sheet form element to reduce the volume of concrete required. In both references, when unrestrained lowermost portions of the flexible sheet form hold fluid concrete, a contact portion of the fabric sheet form is forced into contact with the ground and, when the concrete is solidified carries weight of the building. Hoop stresses are generated in the fabric sheet form and the sheet develops curved bulging marginal portions which extend upwardly and outwardly from the contact portion to upper portions of the fabric sheet which are supported. Thus voids are formed between the marginal portions and the site surface and therefore the contact portion always has a width which is less than maximum or overall width of the footing due to the outwardly bulging marginal portions. Because building load is transferred to the ground only through the contact portion, and not through the bulging marginal portions, concrete in the marginal portions is not used efficiently to transfer load to the ground and thus represents a waste of concrete. Hoop stresses in the fabric increase and width of the contact portion decreases as the concrete mixture is made more fluid, and thus wastage of concrete can become excessive. In addition, the fabric of the sheet form element does not permit concrete to pass therethrough, and thus relatively small voids can be formed between the contact portion of the sheet and the ground immediately beneath the contact portion, thus reducing shear strength between the foundation itself and the ground. If the sheet has a low friction surface, shear strength is reduced still further, which can cause problems during seismic activity.
The invention reduces the difficulties and disadvantages of the prior art by providing a building foundation form apparatus which can be quickly installed on a building site for considerably less cost than conventional foundation forms. In addition, volume of concrete used can be much less than that used with conventional rigid forms and the flexible fabric sheet forms disclosed in said prior art references. Installation costs are reduced because the invention provides a plurality of pre-fabricated form supports which can be assembled quickly and easily, accurately aligned, and readied for concrete pouring in a fraction of the time required for conventional foundation forms.
The invention uses a flexible sheet form element which is supported by the form supports and is used to contain and partially shape the concrete, and prevent contamination of the form supports with the concrete. Lower portions of the flexible sheet form element can deform to accommodate undulations in the building site surface and sloping sites to a far greater degree than those that can be accommodated using conventional rigid sheet concrete foundation forms and thus requires minimal excavation. When the concrete is set, the form supports can be removed quickly, leaving the flexible sheet form element in place as it is of relatively low cost. The form supports, being free from contamination of concrete, are available for reuse. Thus the concrete form apparatus is mostly reusable and this essentially eliminates waste of most of the form material at the building site. In addition, selected portions of the flexible sheet form element are provided with controlled discharge portions with openings which permit passage of concrete therethrough onto the building site surface. This forms a connection between the site surface and the foundation material within the flexible sheet form element, increasing shear resistance between the foundation and the site surface. In addition, concrete discharged from bulges of the marginal portions essentially fills the voids between the bulges and the site surfaces, thus increasing effective footing width and improving utilization of the concrete.
A building foundation form apparatus according to the invention comprises at least first and second transverse form supports, at least first and second longitudinal form supports, and a flexible sheet form element. The first and second transverse form support are adapted to be supported directly on the ground and are longitudinally spaced apart along a longitudinal foundation axis. The first and second longitudinal form supports are adapted to be located on opposite sides of, and substantially parallel to, the foundation axis. Each longitudinal form support is connectable to said at least two transverse form supports so that each longitudinal form support is locatable at a position above the ground. The flexible sheet form element has first and second longitudinally extending edge portions and a contact portion located between the edge portions. Transverse spacing between the edge portions defines width of the sheet form element when flattened. The first and second edge portions are securable to the first and second longitudinal form supports respectively. In this way, the sheet form element is supportable partially by the longitudinal form supports and can lie substantially along the foundation axis. The width of the sheet form element is such that most of the contact portion thereof is at least partially supportable on the ground when the flexible sheet form element is deformed into a generally U-shape and receives a flowable and settable foundation mixture.
A building foundation according to the invention comprises a foundation form apparatus and a set foundation mixture contained therein, the form apparatus comprising at least first and second transverse form supports, at least first and second longitudinal form supports and a flexible sheet form element. The first and second transverse form supports are supported directly on the ground and are longitudinally spaced apart along a longitudinal foundation axis. The first and second longitudinal form supports are located on opposite sides of, and substantially parallel to, the foundation axis. Each longitudinal form support is connected to said at least two transverse form supports so that each longitudinal form support is located at a position above the ground. The flexible sheet form element has first and second longitudinally extending edge portions and a contact portion located beneath the edge portions. The first and second edge portions are secured to the first and second longitudinal form supports respectively so that the sheet form element is deformed into a general U-shape to contain the foundation mixture. The sheet form element is at least partially supported by the longitudinal form supports and lie substantially along the foundation axis. The sheet form element has a width such that most of the contact portion is at least partially supported on the ground.
A transverse form support according to the invention is for use in the foundation form apparatus and comprises first and second legs and a leg tie. The first and second legs have upper and lower leg portions, each lower leg portion has a base portion to resist ground penetration, and each upper portion has a form connector. The leg tie extends between the upper portions of the legs to connect the legs together, and is adjustable substantially vertically along the legs. The leg tie is disposed generally perpendicularly and rigidly to the upper portions of each leg.
A flexible sheet form element is for use in a foundation form apparatus to receive a flowable and settable concrete mixture, the flexible sheet form element comprising a flexible sheet and means to control fullness of the flexible sheet. The flexible sheet has first and second parallel longitudinally extending edges and an adjacent respective edge portion, and a contact portion located between the edge portions. The means to control fullness of the flexible sheet is to maintain adequate footing widths when the sheet is supported along the edge portions thereof to receive the foundation mixture. The means to control fullness of the sheet comprises a longitudinally extending center line disposed symmetrically of the edges of the flexible sheet and symmetrically of the contact portion, and first and second sets of longitudinal guidelines located in the first and second edge portions respectively, each set having a plurality of laterally spaced apart guidelines disposed parallel to the centre line. Each guideline of the first set is identifiable with an equivalent guideline of the second set to form a pair of equivalent guidelines which are spaced equally from the centre line.
Another embodiment of a flexible sheet form element is for use as a foundation form to receive a flowable and settable foundation mixture and comprises a flexible sheet having at least one controlled discharge portion which can pass therethrough at least a portion of the foundation mixture.
A method of installing a building foundation according to the invention, comprises the following steps: supporting at least first and second transverse form supports directly on the ground and spaced apart along a longitudinal foundation axis; locating at least first and second longitudinal form supports on opposite sides of the foundation axis, and connecting each longitudinal form support to said at least two transverse form supports so that at least one longitudinal form support is positioned above the ground on each side of the foundation axis and extends between the transverse form supports; connecting first and second longitudinally extending edge portions of a flexible sheet form element to the first and second longitudinal form supports so that the sheet form element is deformed into a general U-shape and extends longitudinally between the first and second transverse form supports, and laterally between the first and second longitudinal form supports and is at least supported partially by the longitudinal form elements; and pouring a settable, flowable foundation mixture into the at least partially supported flexible sheet form element so that most of a contact portion of the flexible sheet form element is at least partially supported on the ground when the flexible sheet form element deforms into the general U-shape due to weight of the settable, flowable foundation mixture.
Another method of installing a building foundation comprises the following steps: supporting portions of a flexible sheet form element above the ground, the sheet form element being deformed to produce a foundation form and having a contact portion to contact the ground; pouring a flowable and settable foundation mixture into the flexible sheet form element to be mostly contained within the foundation form; permitting controlled discharge of a portion of the foundation mixture from inside the form element through a controlled discharge portion thereof onto the ground to produce a connection therewith.
A detailed disclosure following, related to drawings, describes apparatus and method of several embodiments of the invention, which apparatus and method are capable of expression in structure and method other than those particularly described and illustrated.